The present invention is directed to a system and method for actuating an engine valve. More particularly, the present invention is directed to a system and method for actuating the valves in an internal combustion engine.
An internal combustion engine, such as, for example, a diesel, gasoline, or natural gas engine, typically includes a series of intake and exhaust valves. These valves may be actuated, or selectively opened and closed, to control the amount of intake and exhaust gases that flow to and from the combustion chambers of the engine. Typically, the actuation of the engine valves is timed to coincide with the reciprocating movement of a series of pistons. For example, the intake valves associated with a particular combustion chamber may be opened when the respective piston is moving through an intake stroke. The exhaust valves associated with the particular combustion chamber may be opened when the respective piston is moving through an exhaust stroke.
The combustion process of an internal combustion engine may generate undesirable emissions, such as, for example, particulates and oxides of nitrogen (NOx). These emissions are generated when a fuel, such as, for example, diesel, gasoline, or natural gas, is combusted within the combustion chambers of the engine. If no emission reduction systems are in place, the engine will exhaust these undesirable emissions to the environment.
An engine may include many different types of emission reduction systems to reduce the amount of emissions exhausted to the environment. For example, the engine may include an engine gas recirculation system and/or an aftertreatment system. Unfortunately, while these emission reduction systems may effectively reduce the amount of emissions exhausted to the environment, these systems typically result in a decrease in the efficiency of the engine.
Efforts are currently being focused on improving engine efficiency to counterbalance the effect of emission reduction systems. One such approach to improving engine efficiency involves adjusting the actuation timing of the engine valves. For example, the actuation timing of the intake and exhaust valves may be modified to implement a variation on the typical diesel or Otto cycle known as the Miller cycle. In a xe2x80x9clate intakexe2x80x9d type Miller cycle, the intake valves of the engine are held open during a portion of the compression stroke of the piston.
The engine valves in an internal combustion engine are typically driven by a cam arrangement that is operatively connected to the crankshaft of the engine. The rotation of the crankshaft results in a corresponding rotation of a cam that drives one or more cam followers. The movement of the cam followers results in the actuation of the engine valves. The shape of the cam governs the timing and duration of the valve actuation. As described in U.S. Pat. No. 6,237,551, a xe2x80x9clate intakexe2x80x9d Miller cycle may be implemented in such a cam arrangement by modifying the shape of the cam to overlap the actuation of the intake valve with the start of the compression stroke of the piston.
One problem with implementing a Miller cycle in an engine is that the resulting reduced air flow and compression ratio may negatively impact the performance of the engine under certain operating conditions, such as, for example, when the engine is starting or operating under heavy loads. In these types of conditions, engine performance may be enhanced by switching the operation of the engine to a convention diesel cycle. This may be accomplished with a variable valve actuation system, such as the system described in U.S. Pat. No. 6,237,551. As described, the variable valve actuation system may include a valve that is operable to selectively enable and disable a Miller cycle.
While the selective enabling of a Miller cycle may improve the performance of an engine, the variable valve actuation system may also increase the amount of required maintenance on the engine. If, for example, a variable valve actuation system were to fail and cause an engine to continuously operate in a conventional diesel cycle, the resulting increased compression ratio in each cylinder may eventually damage the engine.
The engine valve actuation system and method of the present invention solves one or more of the problems set forth above.
One aspect of the present invention is directed to an engine valve actuation system that includes an engine valve moveable between a closed position and an open position. A spring is operatively connected to the engine valve to bias the engine valve towards the closed position. An actuator is operatively connected to the engine valve and is operable to selectively engage the engine valve to prevent the engine valve from returning to the closed position and to release the engine valve to allow the engine valve to return to the closed position. A sensor is configured to provide information related to the operation of the actuator. A controller is configured to transmit a signal to the actuator to engage the engine valve to prevent the engine valve from returning to the closed position and to release the engine valve to the allow the engine valve to return to the closed position. The controller is further configured to receive a signal from said sensor and to identify when the actuator fails to engage the engine valve in response to the transmitted signal or when the actuator fails to release the engine valve.
In another aspect, the present invention is directed to a method of controlling an engine valve. A cam assembly is operated to move an engine valve between a closed position and an open position. A signal is transmitted to engage an actuator with the engine valve when the engine valve is at least partially open to prevent the engine valve from returning to the closed position and to release the engine valve to allow the engine valve to return to the closed position. An identification is made when the actuator fails to engage the engine valve in response to the transmitted signal or when the actuator fails to release the engine valve.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.